While the "Big Three" have largely continued to control men's tennis in the years since Rio, women's tennis has seen titles spread among a number of top players.
Who's back: Four-time Olympic gold medalist Serena Williams gave birth to her daughter in September 2017, experienced harrowing complications, and returned to Grand Slam tennis at the 2018 French Open. Williams has twice advanced to the final in pursuit of her first Grand Slam win since having a child, and No. 24 overall. Venus Williams, the most decorated Olympic tennis player in history, currently has an outside chance to return.
Rio women's singles gold medalist Monica Puig, who entered those games unseeded and won Puerto Rico's first Olympic gold, plans to play. Germany's 2016 silver medalist Angelique Kerber will be in Tokyo, as will bronze medalist Ptra Kvitova (CZE). Rio fourth-place finisher Madison Keys (USA) is also currently in contention.
On the men's side, it's not yet clear if Great Britain's two-time defending Olympic champion Andy Murray will make the cut. 2016 silver medalist Juan Martin Del Potro is targetting Tokyo for a comeback from a series of knee injuries.
If healthy, Switzerland's Roger Federer also plans to seek the Olympic singles title that's eluded him through four berths so far -- he missed Rio because of a knee injury. Serbia's Novak Djokovic, too, will seek his first Olympic singles gold, while Spain's Rafael Nadal is in the hunt for this third.
Rio bronze medalist Kei Nishikori is also in the running to play in front of a home crowd in Tokyo.
Who's gone: Russia's Ekaterina Makarova, who won the 2016 women's double title along with Elena Vesnina, retired in 2020. London 2012 men's doubles champions Bob and Mike Bryan, who withdrew from Rio over health concerns, also retired last year.
New faces to watch: Technically a new star since Rio, although she's already a household name, Japan's Naomi Osaka is shaping up to be one of the biggest names at her home Olympics. Osaka has picked up four Grand Slam titles since 2018, become a near-universal fan favorite, and was one of the highest-earning athletes in the world in 2020.
For the U.S., 2020 Australian Open winner Sofia Kenin currently leads all potential qualifiers. Former UCLA player Jennifer Brady is also in the running, having recently made the rare jump from college to professional success and making her first major final at the 2021 Australian Open (where she lost to Osaka).
Australia's Ashleigh Barty, the current World No. 1, and Canada's Bianca Andreescu plan to play, as does Simona Halep, who pulled out of Rio over concerns about the Zika virus.
Russia's Daniil Medvedev, who's made two major finals in the last two years, intends to play in Tokyo. Greece's Stefanos Tsitsipas, who made his first ATP final in 2018, also plans to play.